The present invention relates to a lens molding die and a producing method therefor.
It has been known to produce a lens such as a plastic lens by injection-molding of a resin material. In this way of production, required are a pair of molding dies made of metal or glass and a spacer to be arranged between the dies to form a molding space therebetween. The one surface of respective lens molding die is formed to have a predetermined shape corresponding to that of the respective surface of a lens to be produced. A through-hole for injecting a resin material into the molding space is formed on a spacer.
In the lens fabricating process with the above explained items, a pair of lens molding dies are disposed with the lens forming surfaces thereof opposing to each other and securely contacted, by means of clamping or the like, with placing a spacer therebetween to form a closed space corresponding to the shape of a lens to be produced.
Then, lens material is injected into the closed space through the though-hole of the spacer, and energy is applied to the lens material in the closed space externally, by means of heat, ultra-violet rays or the like, to harden it. Thereafter, the hardened material, i.e., the produced lens is taken out of the molding dies by disassembling them. The molding dies and the spacer are re-used after washing, smoothening and so on.
In accordance with the above explained conventional method for producing a lens, a pair of lens molding dies are occupied for producing one lens until the lens material therein is hardened, so that a large number of molding die pairs must be prepared in order to carry out a mass-production with the above method. However, it costs much to produce a molding die of metal or glass having a molding surface of a precise shape.
Further, as it is necessary for re-using them to take the steps of washing, smoothening and so on, the molding surfaces of the dies are more or less mechanically damaged and/or destroyed while repeating these steps, which causes shortening the life time of the dies.
Accordingly, the cost for producing lenses increases due to the high cost and the short life time of the molding dies, resulting in high prices of the produced lenses.
In the meantime, aspherical lens have recently been widely employed and it has been desired to carry out mass-production for aspherical lenses which are of complex shapes. In order to produce aspherical lenses, the molding surface of a die must be processed to be of aspherical shape, which requires, however, expensive processing machine, high processing technique and long processing time. Thus, the lens molding dies therefor and the resulting lens products become particularly expensive.